This invention relates generally to tuning systems, and more particularly to driving internally mounted channel indicators for detented type tuning systems.
Present day television tuners generally employ a detented selector shaft for selecting the television channel to be viewed. A hollow fine tuning shaft is generally mounted concentrically with the selector shaft. A selector knob is attached to the selector shaft, and a fine tuning knob is attached to the fine tuning shaft.
A channel indicator for indicating the number assigned to the television channel being received is usually provided. For reasons of simplicity, such as indicator is generally attached to or mounted behind the selector knob outside the television set housing. Such indicators have the advantage of relative simplicity, however, due to the limited size of the selector and fine tuning knobs, the channel numbers may be difficult to read or illuminate. As a result, it has become common practice to provide a relatively large indicator inside the television set housing. The numerals on such an indicator may be made much larger than the numerals on an external indicator, and the internal indicator may be readily illuminated, thereby allowing the channel number of the station to which the receiver is tuned to be readily observed from a distance, such as from across the room.
Such internal indicators have always been difficult to drive when a concentric fine tuning system has been employed. This is because the external fine tuning shaft of a concentric fine tuning system covers the internal selector shaft and prevents access to the selector shaft. As a result, prior art systems utilizing an internal indicator have either employed a nonconcentric fine tuning shaft to permit access to the selector shaft, or have extended the selector shaft into the television receiver beyond the length of the fine tuning shaft to permit a gear mechanism to be attached to the protruding end of the selector shaft for driving the indicator.
Neither of the above alternatives has been proven entirely satisfactory. The use of a gear train attached to the end of the selector shaft is not entirely satisfactory because the clearance between meshing gears permits sufficient movement of the indicator with respect to the selector shaft to cause an inaccurate or uncentered display of the channel number. The use of a nonconcentric tuning shaft eliminates the inaccuracies caused by the gear train by allowing the tuning indicator to be connected to the selector shaft directly, but the lack of a concentric fine tuning knob is objectionable to many consumers.
Accordingly, it is an object of the present invention to provide an improved drive mechanism for a television channel indicator.
It is another object of the present invention to provide an improved drive mechanism for a television channel indicator for use with television tuners having a concentric fine tuning shaft.
It is yet another object of the present invention to provide an improved drive mechanism for a channel indicator that displays the number of the channel being received with greater accuracy and at a lower cost than could heretofore be achieved.
In accordance with a preferred embodiment of the invention, a gear mechanism having a driving gear, a driven gear and three planetary gears is provided. The driven gear is attached to the fine tuning shaft and drives the driven gear by means of the three planetary idler gears. The three planetary idler gears are mounted in a housing that is mounted concentrically with the selector shaft and the fine tuning shaft, and attached to the selector shaft for rotation therewith. Because the housing rotates in synchronism with the selector shaft, an indicator may readily be attached to the housing to be driven directly thereby. The use of three planetary idler gears between the driving and driven gears assures smooth operation of the fine tuning shaft and prevents "cogging" effects by providing three equally spaced power transmission paths between the driving and driven gears to assure a uniform application of power to the driven gear.
A star wheel may readily be affixed to the housing for activating a switch such as an AFC defeat switch whenever channels are being changed. The same switch may be coupled to the driven gear in order to defect the AFC during the fine tuning operation.